The invention relates to an apparatus for scanning a radiation-reflective information surface of a record carrier with optical radiation. Such an apparatus comprises a radiation source for supplying a scanning beam, a reflector arranged in the path of the beam for reflecting the scanning beam to the record carrier and an objective lens for focussing the scanning beam to a scanning spot on the information surface.
"Scanning the information surface" as used herein is to be understood to mean both scanning for reading a prerecorded information surface and scanning for recording information in such a surface with a radiation beam which is modulated in intensity in accordance with the information to be recorded.
An apparatus of this type intended for reading an optical record carrier which is provided with an information structure located on an information surface and arranged in information tracks is known from "Philips' Technical Review", Vol. 33, No. 7 (1973) pages 186-189. In the known apparatus, a reflector is arranged in the path of the scanning beam whose central ray extends in a horizontal direction. The reflector reflects the scanning beam in such a manner that the central ray of the reflected beam extends at an angle of 90.degree. to that of the beam incident on the reflector. The record carrier is located above the radiation source and the reflector and the central ray of the scanning beam is perpendicular to the record carrier. The scanning beam is focussed on the information surface by an objective lens which is arranged between the reflector and the record carrier. The reflector is pivotably mounted and is used to correct the position of the scanning spot in the radial direction of the disc-shaped record carrier so that the spot keeps following an information track to be scanned.
More recent developments, particularly in apparatus intended for reading an optical audio record, which are referred to as CD players, have resulted in a compact and elongated read unit which has been described, for example in "Philips' Technical Review", Vol. 40 (1982) no. 6, pages 151-155. This read unit, also referred to as light pen, comprises the radiation source, all the required optical components and the radiation-sensitive detection system and is mounted on a pivotal arm by means of which the radial position of the scanning spot on the information surface can be adjusted. The light pen has a relatively small height, for example 45 mm and is successfully used in present-day CD players designed for home use.
For special uses, for example in portable players or in players to be mounted in motorcars, it is desirable to reduce the mounting height of the optical scanning unit to a considerable extent. To this end, the light pen may be replaced by a scanning unit in which the greater part of the radiation path extends horizontally and in which use is made of a reflector in order to reflect the scanning beam in the vertical direction to the record carrier. However space must still be reserved for the objective lens so that a limit is imposed on the reduction of the distance between the reflector and the record carrier.